[blykins]

Those specs are for:

1. Production camshafts

2. Production engines

Aftermarket cams can have different lash specs and as Barry noted, you can vary those specs to get the engine to behave the way you want.

With the introduction of aftermarket valvetrain, aftermarket rocker arm assemblies, etc., never assume that lash on an iron block/iron head combination will shrink. Always check both cold and hot lash and don't be surprised when it doesn't behave per the older Ford shop manuals.